CA2087385A1 - Reduction of benzene content in gases - Google Patents

Abstract

REDUCTION OF THE BENZENE CONTENT IN FUEL SPECIES Invention by Christine TRAVERS, Patrick SARRAZIN, Jean-Marie DEVES, Jean-Paul BOITIAUX and Pierre AUBOIR The invention relates to a process for reducing the benzene content in gasoline fractions in which one performs a hydrogenation of the charge characterized by: a weight composition comprised in the following intervals:? between 40 and 80% paraffins? between 0.5 and 7% naphthenes? between 6 and 45% aromatics and a maximum distillation temperature between 70 and 90 .degree.C, then an isomerization of the effluent from the hydrogenation, the process being characterized in that one has mixed with said charge and / or said effluent cut C5-C6. Figure to be published

Description

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The invention relates to a method for reducing the content of benzane in gasoline fractions by a process combining the hydrogenation of the benzene contained in the light reformate and possibly the hydrogenation of a Cs-C6 cut and the isomerization of the effluent from 5 the hydrogenation and possibly of said cut.

Environmental problems will jointly lead to reduction in lead content and ~ reduction in benzene content in gasoline fractions, preferably without reduction in octane number.
10 This leads to the need for a rearrangement of the various hydrocarbons present in the essence fractions.

Catalytic reforming used in conditions of severe severity, and the isomerization of normal Cs-C6 paraffins of Saible oclane number are 15 the most commonly used processes currently for obtaining high octane numbers without the addition of lead. The reform process catalytic produces large quantities of high index benzene ., octane This is why it is necessary to develop new proc ~ dice to reduce the benzene tsneur of ess ~ nces while 20 satisfying the specifications on the octane number.

The combination of catalytic reforming and isomerization processes, consisting of separating the Cs-C6 fraction from the reformate, isomerizing it and Introduce it directly into the essence fractions to improve the indication 25 octane is well known: it is described for example in patents US-A-4,457,832, US-A-4,181,599 and US- ~ -3,761,392. Treatment with isomerization of the Cs-C6 cut resulting from the direct distillation of crude oil, is also well known. It leads to a considerable improvement in The octane number of said cut. Reducing the benzene content of 30 reform1 can also be carried out in different ways, such as by example the modification of the naphtha cutting point between reforming and isomerization or separation of the reformate into two fractions: a reformate heavy and a light reformate in which all the benzene is concentrated This light fraction is then sent to a hydrogenation unit which 35 transforms benzene into naphthenes, which are then decycled ,:,. . . :
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21 ~ 7 ~ 85 in an isomerization unit working under severe conditions. The normal paraffins thus formed are isomized by a conventional process isomerization (US-A 5,003,118). In the case of a catalyst of isomerisatian based on chlorinated alumina, naphthenes adsorb on the 5 catalyst and thus contribute to deteriorate its activity.

US-A-3,611,117 describes also ~ a process for hydro-isomerization of cyclic hydrocarbons which uses a metal from group Vlll supported on zeolite as a catalyst for opening cycles in 10 severe operating conditions and as an isomerization catalyst in mild operating conditions.

One of the major problems in reducing the benzene content by saturation followed by decyclization and isomerization of the para ~ ines formed is 5 ~ a diminu1ion possibie of the octane number of char ~ e.

The object of this inven ~ ion is to jointly achieve the reduction of the benzene content in the light reformate and the isomerization of paraffins contained ~ s on the one hand in this light reformate and on the other hand in 20 a Cs-C6 cut generally paraffinic and resulting from direct distillation.

The process of the present invention therefore comprises the hydrogenation of benz ~ ne contained in the charge defined below in a zone hydrogenation and then isomerization of the effluent from the hydrogenation in 25 an isomerization zone, the process being characterized in that one melan ~ e to said charge eVou audit effluent a C5-C6 cut.

Surprisingly, the joint treatment in the isomerization zone of these two possibly hydrogenated charges leads to the obtaining of an effluent 30 almost completely free of benzane and having an octane number high enough that it can be directly incorporated into essencss fractions after stabilization.

The hydrogenation zone and the isomerization zone according to the invention can 35 be included in the same reactor, or in separate reactors 20 ~ 738 ~

such that each of said zones is included in at least one r ~ actor. Of more, the conditions under which the hydrog ~ nation are carried out and isomerization (ie the operating conditions, ie catalyst ..., are ies conditions known to those skilled in the art. They are nevertheless specified 5 below.

The charges concerned by the present invention are generally ~ rally following:

10 - the light fraction of the reformate, - a Cs-C6 cut generally resulting from direct distillation.

The light fraction of the reformate is obtained by distillation of the said reformate. The maximum temperature of distillation of this SJacti ~ n plug is between 70 ~ t 90 C, preferably between 77 and 83 C. The weight composition by hydrocarbon families of this light fraction of the reformate is variable at the following intervals:

- paraffins: between 40.0 and 80.0%, 20 - naphthenes: between 0.9 and 7.0%, - aromatic: between 6.0 and 45.0%.

Benzene is generally the only compound aromatic included in said fraction.
Furthermore, the said fraction may comprise between 1 and 3% of hydrocarbons ol ~ finiques.

On the other hand, the light fraction of re ~ ormat as described above generally has the following characteristics:

, ~ 7385 - 19 average molecular weight is included ~ ntr ~ 70 and 90 g / mol., - the density, measured ~ 15C, is between 0.670 and 0.780 g / cm3, .. ^ ~
- the value of the research octane number is generally between 75 and 90.

Any other hydrocarbon feedstock from another process or set of processes and having characteristics similar to those described above above can also be used.
The weight composition of the Cs-C6 cut generally obtained from the direct distillation, is variable. It depends on the nature of the crude to be treated in the case where the Cs-C6 cut comes from direct distillation.

15 It may contain very low contents of compounds comprising 4 atoms of carbon per molecule (less than 0.5% by weight).

The paraffin content of said cut is generally greater than 90%
weight, its napht ~ nes content generally less than 10% by weight and the 20 benzene content generally less than 1.5% by weight. His index typically research octane is between 60 and 75.

These two types of loads can be sent together in the zone of hydrogenation, the light reformate content of the feed entering the 25 hydrogenation zone ~ both between 10 and 90% and pr ~ féré
between 20 and 80%.

Preferably, the Cs-C6 cut is mixed with the effluent from hydrogenation, that is to say with the saturated light reformate leaving the zone 30 hydrogenation, the effluent content from the hydrogenation of the feed entering the isomerization zone ~ between 10 and 90% and preferably between 20 and 80%.

Whatever the load envisaged, the pressure required for this stage Hydrogenation is generally between 1 and 60 bar absolute, partic ~ rem ~ nt entr ~ 2 and 50 bar e ~ more aYanta ~ euse entr6 5 and 45 bar.

The operating temperature is generally between 100 and 400 C, more advantageously between 150 and 350 C and preferably between 160 and 320 C.

The space velocities calculated with respect to the catalyst are generally between 1 and 50 h-1 and more particularly between 1 and 30 h 1 (volums load per volume of catalyst and per hour).

The flow of hydrogen ~ ne, relative to the catalyst, is generally between 1 and 2000 volumes (gas under normal conditions) per volume of catalytic converter and per hour.
The heat released at this stage is advantageously used to prbchauffar the load of isomerization.

The catalyst used in the hydrogenation zone according to the process of present invention comprises at least one metal M chosen from the group form ~ by nickel, platinum and palladium, used ~ as is or preferably d ~ posb on a support. Mbtal M must be in reduced form at less for 50% of its totality. Preferably nickel or platinum is used, and even more preferably platinum.
~ 5 When using platinum or palladium the catalyst may contain advantageously at least one halogen in a proportion by weight per ratio to the catalyst of between 0.5 and 2%. Preferably, we uses chlorine or fluorine or a combination of both in a proportion relative to the total weight of catalyst of between 0.5 and 1.5%.

In the case of the use of nickel, the proportion of metal M relative to the total weight of catalyst is between 0.1 and 60%, more particularly between 5 and 60% and preferably between 5 and 30%. In the case of The use of platinum and palladium, the total proportion of metal M by .

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relative to the total weight of catalyst is between 0.1 and 10% and so preferred between 0.05 and 5%.

The support can be chosen from the group formed by alumina, silica-aluminas, silica, zeolites, activated carbon, clays and aluminous cements. An alumina is preferably used, with a specific surface at less equal to 50 m ~ / g and d0 pore volume at least equal to 0.4 cm3 / g per example of specific surface area between 50 and 350 m2 / g and volurne porous between 0.4 and 1.2 cm3 / g.
The effluent from hydrogenation shingles generally contains less 0.1% aromatics and generally has between 4 and 6 octane points less than the load entering said area.

The isomerization zone is fed by the effluent from the zone of hydrogenation alone, comprising the light reformate mixture plus the cut Cs-C6 hydrogenated, or by a light reformate mixture plus cut C: s-C6 no hydrogenated. Isomerization is generally implemented in said isomerization zones under the following usual conditions: the temperature is between 150 C :: and 300 C and preferably between 230 and ~ 80 C, and the partial pressure of hydrogens is between the pressure atmospheric and 70 bar and preferably between 5 and 50 bar. Speed space is between 0.2 and 10 liters and preferably between 0.5 and 5 liters of liquid hydrocarbons per liter of catalyst per hour. The hydrogen / charge molar ratio is normally between 0.5 and 10 and preferred between 1 and 3.

The catalyst used in the isomerization zone according to the process of present invention may be a catalyst based on platinum on alumina chlorinated, said alumina containing from 1 to 10% of chlorine and so preferably 2 to 9% chlorine, but preferably use a catalyst comprising at least one metal from the Vill group and a zeolite. Di ~ ferentes zeolites can be used for said catalyst such as for example lamordenite or ka zeolite Q. A mordenite is preferably used ~ e having a Si / AI (atomic) ratio between S and 50 and preferably between -2a87 ~ 85 5 and 30, a sodium tsneur lower than 0.2% and pre-r ~ e way less than 0.1% (relative to the weight of dry zeolite), a volume of mesh V of the elementary mesh between 2.78 and 2.73 nm3 and of preferably between 2.77 and 2.74 nm3, an absorption capacity of 5 benzene greater than 5% and preferably greater than 8% compared to dry solid weight). The mordenite thus prepared is then mixed ~ e with a generally amorphous matrix (alumina, silica alumina, kaolin, ...) and form by any method known to those skilled in the art (extrusion, pelletizing ~, The ~ eneur en mord ~ nite of the ainsl support obtained must be 10 greater than 40% and preferably greater than 60% by weight At least one hydrogenating metal from the Vlll group, preferably selected in the ~ roupe formed ~ by platinum, palladium, and nickel, is then deposited on ~ suppo ~, s ~ it s ~ us f ~ rme d ~ compl ~ xe t ~ tramine pa ~ ~ c ~ an ~ e cationic, 15 either in the form of hexachloroplatinic acid in the case of platinum ~ or in the form of palladium chloride by anion exchange.

In the case of platinum or palladium, the content by weight is between 0.05 and 1% and preferably between 0.1 and 0.6 / O. In the case of nickel the 20 weight content es ~ between 0.1 and 10% and preferably between 0.2 and 5%

The effluent obtained at the exit from the isomerization zone has an index octane high enough to be incorporated into gasoline fractions after 25 stabilization and includes maximum benzene content generally ~ scab ~ 0.1% by weight Preferably, it is completely free of benzene The single figure shows an arrangement of the method according to the invention, in which hydrogenation and isomerization are carried out in two reactors 30 (or separate) units The stabilized reformate (1) is sent to a distillation column (6), which a heavy reformate (3) comes out at the bottom which can be used directly in the essence fractions and at the top a slight reformate (2) The latter is sent to 35 a hydrogenation unit (7), alone or after mixing with at least one :
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part (9) of a Cs-C6 cut from direct distillation. The cup obtained ~ 4) is treated ~ c in an isomerization unit ~ (8) giving the product ~ inal (5) which, after stabilization, can be incorporated into the gasoline fractions.
Optionally at least part (10) of the Cs-C6 distillation cut direct is mixed with saturated light reformate (4) just before the unit isomerization (1 0).

The two examples which follow specify the invention without limiting its scope.
The hydrogenation and isomerization actions are carried out in said examples in two separate reactors (or units).

Example 1 (according to the invention) The reformate obtained after distillation at 85 ° C., containing 21.5% of ~ enzyme and having an octane number of 80.3 is mixed at the rate of 50% by weight with a Cs-C6 cut of direct distillation containing 0.7% of benz ~ ne and having an octane number of 65. The compositions da 2 products are listed in Table 1. The charge from the mixture, including the composition also appears in table 1, is sent in a unit hydrogenation at a temperature of 110C, and a pressure ds 40 bar. The molar ratio hydrogen to hydrocarbons contained in the charge sst equal to 0.85, and the liquid space velocity is equal to 4 h -1. The catalyst used in the hydrogenation section consists of 15% of Ni deposited on alumina.
The effluent from the hydrogenation unit, the detailed composition of which appears in Table 1, no longer contains benzene but has an octane number of 70.9. It is then sent to an isomerization unit operating at a temperature of 260C, a pressure of 30 bar with an LHSV equal to 2 h -1 and a hydrogen to hydrocarbon molar ratio of the charge of the isomerization unit equal to 4. The catalyst used in the unit of isomerization contains 0.3% of Pt deposited on a support composed of 80% mordenite with Si / AI ratio = 11 and 20% alumina. The effluent released from the isomerization unit to the composition given in Table 1; he ... not : `` '.

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contains more benzene and has an octane indic ~ d0 78.1. It is therefore directly incorporated into the gasoline reactions after stabilization.

.
R ~ tormat Coupe Char ~ e de Effluent de Eltluent de Cs-C6 of hydro ~ é- hydro I ~ - I'lsomérl-dlstlllatlon natlon natlon satlon light 6.5 1.0 3.7 3.7 4.6 iC5 9.9 18.9 14.4 14.4 18.8 nC5 7.1 25.4 16.25 16.25 12.5 22DMC4 3.0 0.4 1.7 1.7 6.3 23DMC4 4.1 1.85 3.0 3.0 4.8 2MC5 15.8 11.1 13.45 13.45 17.6 3MC5 t 2.5 9.4 1 t, 0 11, û 11.55 nC6 12, ~ 19.6 15.9 15.9 8.75 C7 3.5 4.4 3.9 3.9 1.9 CC5 0.4 1.4 0.9 0.9 0.9 MCC5 3.6 4.1 3.85 3.85 9.9 Benz ~ n ~ 21.5 0.7 11.1 CC6 0 1.75 0.85 11.95 2.4 RON80.3 65 72.9 70.9 78.1 Table I

Example 2 (according to the invention) The light reformate obtained after distillation at 85 ° C. containing 21.5% of benzene, with an octane number of 80.3 and the composition of which detailed is given in table ll, is sent to a hydrogenation unit at a temperature of 110 (:: and a pressure of 40 bar. The molar ratio hydrogen on hydrocarbons contained in the charge is equal to 0.85, and the 15 liquid space velocity is 4 h -1. The catalyst used in the section hydrogenation consists of 15% Ni deposited on alumina.

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The effluent from the hydrogenation unit, the detailed composition of which does not contain benzene, but has an octane number of 76.5. It is then mixed at 50% by weight with a Cs-C6 cut of direct distillate containing 0.7% benzene and showing an index 5 octane 65. The composition of this cut as well as the composition of mixture which constitutes the charge of the isomerization unit are given in table ll. The isomerization unit operates at a temperature of 260 ° C, a pressure of 30 bar with an LHSV ~ scab ~ 2 and a molar ratio ~
hydrogbne on hydrocarbons of the load ~ gal to 4. The catalyst used ~ in 10 this unit of isomerization contains 0.3% of Pt deposited on a support composed of 80% mordenite with Si / AI ratio = 11 and 20% alumina The effluent leaving the isomerization unit has the composition given in the table ll; it no longer contains benz ~ ne and has an octane number of 78.1 ~ This effluent can be directly incorporated into the gasoline fractions 15 after s ~ abilisa ~ ion, Re ~ ormatCoupe E111uent de Charge de E1fluent do C5-c6 of hydro ~ I'lsomérlsatlonI'lsom ~
_ dlstlllatlon ~ natlon rlsatlon Ibgers 6.5 1.0 6.5 3.7 4.6 iC5 9.9 18.9 9.9 14.4 18.8 nC5 7.1 25.4 7.1 16.25 12.5 22DMC43.0 0.4 3.0 1.7 6.3 23DMC44, 1 1.85 4, 1 3, 0 4.8 2MC5 15.8 11.1 15.8 13.45 17.6 3MC5 12.5 9.4 12.5 11.0 11.55 nC6 12.1 19.6 12.1 15.9 8.75 C7 3.5 4.4 3.5 3.9 1.9 CC5 0.4 1.4 0.4 0.9 0.9 MCC5 3.6 4.1 3.6 3.85 9.9 Benzene 21, 5 0.7 0.35 CC6 0 1, 75 21, 5 1 1, 6 2.4 _ RON 80.3 65 76.5 _ 71.2 78.1 Table ll

Claims (8)

1- Process for reducing the benzene content in fractions essences in which, in a hydrogenation zone, a charge hydrogenation characterized by:
a weight composition in the following ranges:

? between 40 and 80% paraffins ? between 0.5 and 7% naphthenes ? between 6 and 45% aromatics and a maximum distillation temperature between 70 and 90 ° C, then an isomerization, in an isomerization zone, of the effluent from of hydrogenation, the process being characterized in that one mixes a C5-C6 cut at least to one of the hydrocarbon cuts following:

? Said charge, ? Said effluent. 2- The method of claim 1 wherein the mixture comprises 10 to 90% of said hydrocarbon cut. 3- Method according to one of claims 1 or 2 wherein the catalyst of hydrogenation comprises at least one metal chosen from the group formed by nickel, platinum and palladium. 4- Method according to one of claims 1 to 3 wherein the catalyst of isomerization includes a mordenite of Si / AI ratio between 5 and 50 and at least one group VIII metal. 5- The method of claim 4 wherein the group VIII metal is chosen from the group formed by platinum, palladium and nickel. 6- Method according to one of claims 1 to 5 wherein the hydrogenation is carried out under the following operating conditions: the temperature is between 100 and 400 ° C, the pressure is between 1 and 60 bar, the space speed is between 1 and 50 volumes of charge per catalyst volume per hour and the hydrogen flow rate is understood between 1 and 2000 volumes per volume of catalyst and per hour. 7- Method according to one of claims 1 to 6 wherein the isomerization is done according to the following operating conditions: the temperature is between 150 and 300 ° C, the partial pressure of hydrogen is between atmospheric pressure and 70 bar, the space speed is between 0.2 and 10 liters of charge per liter of catalyst and per hour, and the hydrogen to charge molar ratio is between 0.5 and 10, 8.- Method according to one of claims 1 to 7 wherein the section C5-C6 is a direct distillation cut.